Process of preserving wood



Patented Apr. 26; 1932 LEO 1?. CURTIN, OF CRANLBUBY NEW JERSEY raoc'nss or ransnnvme "woon No Drawing. Application filed April 12,

This invention resides in an improvement in the process of treating wood and other cellulosic materials by impregnating them with an aqueous preservative, such as an 5 aqueous solution of zinc metaarsenite or connection therewith, although, as will appear hereinafter, it-is by no means limited thereto. a

In certain sections of the country, particularly in the so-called arid regions. it has been found that the mechanical life of a cross-tie is prolonged by a coating orimpregnation of a hydrocarbonoil. In such localities, an un-- treated tie has'a tendency to split. check or bloom and is frequentlyremoved from service because of mechanical or physical deterioration before any appreciablede'cay or fungus or insect attack has occurred.

petroleum oil coating or impregnation is believed to be the retarding effect of the oil on the rate of change of the moisture content of the wood. During a period of rainfall, or of high relative-humidity, the water absorption of an oil-soaked timber is less than that of a similar untreated "specimen. Conversely, during a period of low relative humidity, the rate of'loss of moisture from the oil-treated timber is lower than from a similar untreated specimen.

When wood loses moisture, it shrinks and as the outer portion of the wood becomes dry before the interior portion, strains are set up by the shrinkage of the outer portion which can be relieved only by cracking or checking. It follows, therefore, that the presenceof an conditions will tend to keep the outer and inner portions of the wood more nearly in equilibrium with respect to moisture content and prevent a great deal of the cracking and checking which otherwise would take place. It is believed, also, that the presence of oil The principal benefit derived from the -method of treating wood first with an aqueoil on wood which is exposed to rapid drying 1930. Serial N0. 443,933.

increases the resistance cal shock.

Experience has indicated. that certain fractions of petroleum are particularly well adapted for protectively coating and impregnating wood, a residuum oil of high asphalt content being particularly desirable. The protection afforded by such an oil is due in part'to inert and very permanent substances produced by the oxidation and polymerization of asphaltic bodies present in the oil.

If the aqueous preservative consists of zinc meta-arsenite dissolved'in a volatile organic acid, such as acetic acid, the wood fiber is saturated with this powerful insecticide and fungicide and, eventually, the-cellwalls of the wood become covered with innumerable small, difiicultly soluble crystals of zinc metaarsenite; Railroad ties protected in this manner against decay and insects and fungus attack and with an outer deposit of oil to retardmechanical deterioration, should last fora great many years even under the most trying conditions.

In'the two-movement process. that is, a

of wood to mechanious .solutionand afterwards with an oil, or vice versa, the presence of asphaltic bodies in the oil usually causes difliculties. Such bodies greatly increase the tendency of the oil and aqueous solution to emulsify. in fact, the asphaltic bodies act as a powerful emulsifying agent and as a stabilizer for water-inoil emulsions. In such emulsions it is considered that the drops of aqueous liquid are surrounded by a spherical shell or film of asphaltic material.

Regardless of whether the oil treatment of the timber follows or precedes the treatment with the aqueous preservative, the oil 'encounters the aqueous solution on the walls of the treating retort, on the surface of the timber being treated, and elsewhere. The solution is usually taken up by the oil with the formation of an emulsion in which the oil is the continuous phase. In the course of the treatment of a number of charges of timber, the oil may take up and emulsify, say 20 to 30% of the aqueous solution and become so other emulsion-forming oil is treated with an oil-soluble reagent having emulsion-breaking or emulsion-inhibiting properties, it is possible to carry on indefinitely the alternate treatments of successive charges of timber with aqueous solution and oil without producing suflicient emulsion to cause operating dithculties.

Asan emulsion-breaking or inhibiting reagent, I prefer to use a tar produced in the low temperature distillation of coal known as low-temperature tar or a fraction thereof. I Such tar differs from the tar produced by the high-temperature process of coal distillation in that it contains a large proportion of cyclo-paraflins and other non-aromatic hydrocarbons and, also, a remarkably high content of phenolic bodies, or tar acids. Such tar acids are, for the most part the homologues of phenol, naphthol and related bodies and usually constitute about one third of the total tar.

A typical low-temperature tar will, on redistillation, give a distillate boiling below 300 C. equal in quantity to one-third of the original material, another third will distill over at temperatures above 300 C. and the remaining third will remain in the retort as coke. The proportion a tendency for the low-boiling fraction to have as high as 35 to 40% of tar acids.

In actual practice, it is preferable, in some cases, to use the undistilled tar as the emulsion inhibitor, in other cases, the entire distillate up to coking temperature and, with certain petroleums, the distillate boiling below 300 C. The nature of therpetroleum determines which material is most advantageous to use.

I am aware that it has been proposed to use I breaker of the petroleumf cresylic acidas a water emulsions produced naturally in the oil fields. In the-presentprocess, however, cresylic acid alone is not desirable since, with many petroleums, and more particularly with zinc ion present in the aqueous solution, it tends to build emulsions 0f the lyophile type, in which oil is the disperse, and water the continuous, phase. The present process can be operated advantageously with all of the cresylic acid removed, but canialso be operated with cresylic acid present.

In the operation of the process, 1 to 5 percent by volume of the crude low-temperature tar is added to the petroleum for the pur-- pose of inhibiting emulsion formation. If

one of the more active fractions is used 0.5 to 2.0 percent is usually sufficient.

In my 443,932 filed concurrently herewith I have described and broadly claimed the use of lowof tar acids in the three I fractions is fairly uniform with.

more particularly the breaking of the socalled oil-field petroleum-water emulsions for the recovery therefrom of their petroleum content.

I claim:

1. In the impregnation of wood with a petroleum oil and an aqueous preservative by the two-movement process the step of preventing-objectionable 'emulsification of the oil and the aqueous liquid by adding to the oil a relatively small amount of at least a portion of low-temperature coal tar containing an active emulsion-inhibiting constituent thereof. I

2. In the impregnation of wood with a petroleum oil containing asphaltic bodies and an aqueous preservative by the two-movement process the step of preventing objectionable emulsification of the oil and the aqueous liquid by adding to the oil a relatively small amount of at least a portion of a low-temperature coal tar containing an active emulsion-inhibiting constituent thereof.

3. In the impregnation of wood with a petroleum residuum oil of high asphalt content and an aqueous preservative by the twomovement process'the step of preventing objectionable emulsification of the oil and the aqueous liquid by adding to the oil a relatively small amount of at least a portion lowtemperature coal tar containing an active emulsion-inhibiting constitutent thereof.

4. In the impregnation of wood with a petroleum oil containing asphaltic bodies and an aqueous preservative containing zinc ions by the two-movement process the step of preventing objectionable" emulsification of the oily and aqueous liquids which consists in adding to the oily liquid about from 1 to 5 percent by volumeof low-temperature coal tar.

In testimony whereof I aflix my signature.

LEO P. CURTIN.

companion application Serial'No. 

